/*
 * JANN - a Java toolkit for creating arbitrary Artificial Neural Networks.
 * 
 * Copyright (c) 2009 Matthijs Snel
 * 
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
package net.jann;

public class SigmoidFunction implements Function {
	
	public double[] eval( double[] x ) {
		double r[] = new double[x.length];
		for ( int i = 0; i < x.length; i++ )
			r[i] = eval(x[i]);
		return r;
	}
	
	public double eval( double x ) {
		return 1 / (1 + Math.exp(-x));
	}
	
	public double[] deriv( double[] x ) {
		double r[] = new double[x.length];
		for ( int i = 0; i < x.length; i++ )
			r[i] = deriv(x[i]);
		return r;
	}
	
	public double deriv( double x ) {
		double s = eval(x);
		return s*(1-s);
	}
}
